VASELINE of purity, and whether it is natural or artificial. The tests made are as follows : 1. Suspended Impurities.—These are recognised by their appearance and are separated by fusing the product and filtering it in an oven. 2. Mineral Matter.—From 0-5 to i gram is burnt in a platinum dish to ascertain if anyweighable residue remains. Any emission of odours of resin or of burnt fats during the combustion should be noted. 3. Solubility in Alcohol. Reaction.—One volume of the vaseline is shaken with two volumes of alcohol, the latter being separated and tested as to acidity or alkalinity and diluted with water to see if it becomes turbid. 4. Behaviour towards Sulphuric Acid.—10 grams of the melted vaseline are heated with 2-5 c.c. of a mixture of 5 parts of water with 15 parts of cone, sulphuric acid on a water-bath for 15 minutes, with frequent shaking, any browning of the acid or vaseline being noted. 5. Detection of Fats.—2 grams of the vaseline are boiled with a few c.c. of caustic soda solution, the cold aqueous layer being subsequently filtered off and acidified with hydrochloric acid : turbidity or separation of solid substance indicates the presence of fats. 6. Detection of Resins.—By Morawski's reaction (see Heavy Oils, Chemical Tests, 7). 7. Viscosity.—By means of Engler's viscometer (see Heavy Oils, Physical Tests, 7), working at 60° C. and keeping also the vessel into which the liquid flows hot. 8. Determination of the Paraffin Wax.—In a thin-walled, glass cylinder, 20 cm. tall and 3-5 cm. wide, a weighed quantity of about 0-5 gram of the vaseline is dissolved in the hot in.3 c.c. of ether, and the solution treated with 50 c.c. of 98% alcohol. After being cooled to o° for an hour and filtered through a filter also kept at o°, washing with a total quantity of 150 c.c. of 98% alcohol maintained at o° (see Figure, p. 338), the insoluble residue is dissolved on the filter in hot benzene and the solution evaporated in a tared glass dish and the residue weighed. If the precipitate formed in the tube by addition of alcohol to the ethereal vaseline solution is not readily detached from the glass (as happens especially with natural vaselines and with those containing ceresine), the adherent part should be dissolved in benzene and this solution added to that previously obtained. * * * Pure vaseline should melt to a clear liquid and should not contain mineral matter, or dissolve appreciably in cold alcohol, or exhibit an acid or alkaline reaction, or turn sulphuric acid brown. According to the Italian Pharma- copoeia, pure vaseline for pharmaceutical use should be perfectly neutral and quite free from fats, and should leave no ash. Natural vaselines have viscosities varying from 4-5 to 7-5 at 60° C. (referred to that of water at 20° C. and determined with the Engler apparatus), whilst the viscosity of artificial vaselines is usually little above i and that of mixtures of natural and artificial vaselines rarely reaches 3-5. Natural vaselines contain 63-80% of solid paraffin insoluble in alcohol, whilst the artificial ones contain only n-35%, and mixtures of the two intermediate proportions. Ethereal solutions of natural vaselines are precipitated by alcohol in the form of a sticky, cheesy mass, the liquid remaining turbid ; with artificial vaselines, a flocculent precipitate is formed, while the liquid remains clear.r.